It is well known that the exhaust emissions from a vehicle may be detected and characterized by a remote sensing system, wherein a rotating device, such as a reflecting wheel or a movable filter is incorporated for allowing one or more detectors to receive a beam with different wavelength bands passing through the emission plume, whereby various gas components of the plume can be analyzed and monitored.
Such a remote sensing system is disclosed in U.S. Pat. No. 5,210,702, in which a collimated beam emitted from a radiation source passes through the exhaust plume of a vehicle and is reflected from an adjustable mirror onto a reflecting wheel therein. The beam is then reflected therefrom to the focusing mirrors thereof and in turn directed at a plurality of detectors through the respective filters.
Another gas analysis device is disclosed in WO 00/42415, wherein a beam emitted from a radiation source passes through an emission plume of a vehicle.
The beam may optionally be focused on a detector by a lens. The light beam also passes through a set of moveable filters before it impinges on the detector. Alternatively, the beam may optionally be focused on a detector by a lens via reflection off of one or more of a moveable set of reflective filters, which may reflect only the wavelengths of specific detection bands of radiation for detection of different components of the vehicle emission plume.
Further, the moveable set of filters may comprise a rotating filter wheel with filters mounted on the wheel. Such filter wheel is mounted for rotation about its axis. Various filters are mounted on the filter wheel; thereby the filter wheel may be rotated on its axis to align different filters with a single detector at different times. Each filter permits only a specific detection band of radiation to reach the detector by transmission or reflection. Each detection band is centered on a wavelength of radiation that is characteristic of the absorption pattern of a specific component of the vehicle emission. Each filter on the wheel passes a detection band of radiation which corresponds to a specific vehicle emission component to be detected. The wheel and therefore the filters, rotate so that multiple vehicle emission components may be sequentially detected and analyzed using a single detector.
However, these systems have some drawbacks. For example, the use of the rotating device render a large number of parts, such as special reflectors, a variety of detectors and light filters to be manufactured, assembled, aligned, maintained, and calibrated for ensuring a proper operation of the system. Needless to say, each of these parts might introduce errors into the final measurements to some extent. For instance, the system may suffer from a light-bleed from edges of the light filters, thereby allowing undesirable wavelengths of light to be received by the detectors. Uncertainty as to the measurements may also occur because different detectors may react differently to the variety of ambient conditions encountered during the operation of these devices.
In addition, these systems can only receive a single response at each time instant, thereby a time lapse (Dt) exists between the responses for different gases components. However, such a time lapse is generally ignored in the calculation of gas components and each data point of the correlation graph for the concentration of any two of the gas components, such as hydrocarbons (HC) and carbon dioxide (CO2), is assumed to be collected at the same time instant, thereby introducing significant errors thereinto. For those instable gas components such as SO2, which tends to be difficult to measure with these systems of prior art due to the rapid changing character thereof, for example, SO2 might easily and quickly react with water and atmospheric oxygen to form sulfuric acid during such a time lapse.
Furthermore, the use of a variety of filters, detectors, reflectors, and the like can add considerable complexity and bulk thereto. In addition, should other components of the emission be detected, the filters and/or detectors thereof also need to be replaced correspondingly, thereby involving considerable cost in parts, as well as in the assembly, alignment, and calibration thereof.
Yet another gas analysis device is disclosed in U.S. Pat. No. 4,678,914, in which a digital IR gas analyzer comprising a sample cell having a conical shaped interior wall and a filter wheel provided with HC, CO and CO2 interference filters is proposed. Wherein an IR radiation from a source is directed toward an IR detector and passes through both a gas located in the sample cell and then one of various light filters mounted on the continuously rotating filter wheel. This device needs to be in close proximity to an emission output for proper operation, and it requires a sample cell for gas analysis. Such requirements are not feasible in the remote sensing of vehicle emissions, for which a sample of the emission needs to be collected and isolated from the same taken in a sample cell. Further, such a device only provides a localized reading of the gas at the exact point where the sample is taken.
There are still more systems and methods for remote sensing the exhaust emissions as disclosed in various patent publications, such as U.S. Pat. No. 5,319,199, U.S. Pat. No. 5,401,967, U.S. Pat. No. 5,591,975, U.S. Pat. No. 5,726,450, U.S. Pat. No. 5,797,682 and US 2005/0197794, each of which is in whole incorporated herein by reference.
Further, various regulations and standards on the emissions had been set forth throughout the world and all the latest automobiles on the road have to meet such stringent regulation or emissions limits thereof. The Bureau of Automotive Repair in the state of California has published a specification of On Road Emission Measurement System (OREMS) in which it lists the requirements for Remote Emission Measurement systems.
In Europe, the Euro 4 limits as specified in the Directive 70/220/EEC regulation as last amended by Directive 98/69/EC (Euro 3/4). Emission limits of Euro 3 are CO 2.3 g/km, HC 0.20 g/km, NOX 0.15 g/km and the same of the Euro 4 are CO 1.0 g/km, HC 0.10 g/km and NOX 0.8 g/km. In Japan the limits for the 10-15 mode test procedure are CO 2.1-2.7 g/km, HC 0.25-0.39 g/km NOX 0.25-0.48 g/km. The new limit introduced will drop these figures to CO 0.67 g/km, HC 0.08 g/km and NOX. The limits for the USA FTP75, SC03, US 06 and highway test procedures changed from CO 3.4 g/mile, HC 0.25 g/mile & NOX 0.4 g/mile in 1994 and to CO 1.7 g/km HC 0.125 g/km NOX 0.2 g/km in 2004. In most cases the reduction is around 50% of the emission limit set forth in the past. Other countries tend to follow or adopt these emission limits and tests procedures for vehicles locally. The new stringent emission limits of new vehicles induce increased difficulty to detect the vehicle plume. Vehicles can still become a polluter if they are not properly monitored or maintained. Having new cars in the fleet means that existing technology of the prior art would be unable to detect these vehicles as well.
In addition, exhaust emission and engine performance of a new vehicle can deteriorate after it has been in operation for a while, without the driver becoming aware of this. On Board Diagnostic (OBD) systems are widely employed in many modern vehicles to detect malfunctions of various components therein and provide a warning signal to the driver normally in the form of a warning light. However such alarms can be ignored or the warning system will fail to operate but the vehicle will still operate seeming without any change.
Modern vehicles comprise a three way catalytic converter with closed loop control. The Engine Control Unit (ECU), also known as Engine Management System (EMS) of the vehicle governs the air-fuel ratio to achieve the ideal stoichiometric ratio. For gasoline fuel, the stoichiometric air/fuel mixture is approximately 14.7 times the mass of air to fuel, i.e., 14.7 kg of air will burn ideally with 1 kg of fuel. This ratio can also be presented in terms of Lambda (λ). Fuel burning at stoichiometric mixture gives a Lambda of 1 (λ=1) at which the catalytic converter will run at its optimum efficiency. However this is not always the case in practice. In operation, the ECU will monitor air intake temperature, pressure, air flow, and numerous other sensors to achieve stoichiometric combustion. Wherein a small sensor (lambda sensor or O2 sensor) inserted into the exhaust system of the engine will measure the concentration of oxygen remaining in the exhaust gas to allow the ECU to control the efficiency of the combustion process in the engine.
Whilst the vehicle engine is running under the closed loop control system the ECU will adjust automatically the quantity of fuel injected into each cylinder of engine with respect to the engine's RPM and the position of the gas pedal or throttle. To achieve stoichiometric combustion, the ECU may have to adjust the fuel intake depending on whether the engine runs rich (λ<1) or lean (λ>1). As the lambda sensor updates the ECU typically every 0.8 second whereby there is a possibility that the engine is not being run within the correct λ value in-between each of 0.8 second interval during which the engine may have had more or less than 40 complete cycles if it runs at 3000 RPM.
There are exceptions to these rules as an ECU program may allow the vehicle to be run in open loop mode under hard acceleration (i.e. to provide extra fuel to help prevent hesitation under acceleration) which may produce higher emissions.
Currently, remote sensing systems in operation have to finish the measurement of a vehicle typically within 0.7 second due to the very short time that the emission or the plume can be measured after the vehicle has passed the system. Such remote sensing systems work well with remote sensing surveys as many cars are evaluated together to obtain a trend of the vehicle fleet emissions being measured. However, it is difficult to determine what operating status the ECU of individual vehicles being tested is currently under, i.e. the ECU can be either in transient (switching between a higher or lower stoichiometric ratio) or open loop state. As it takes time for the vehicle to restore the air-fuel mixture to the stoichiometric ratio when the mixture of air and gasoline going into the engine is rich or lean, a higher than normal exhaust emission might be accidentally sampled from the vehicle while it is passing through the remote sensing device whereby leading to an invalid or incorrect reading for the vehicle.
There are a few testing technologies being employed to test vehicle emissions. Such as stationary Idle Emission Test wherein a multi-gas analyzer, for example a four gas analyzer probe is inserted to the exhaust pipe and measures the exhaust gas with the vehicle running at idle. In the Chassis Dynamometer Test (IM240 in the USA), a vehicle is driven on a chassis dynamometer over a set of drive cycles for between 90 and 240 seconds. Dilute exhaust emission samples are extracted and measured by a complex system analyser and Constant Volume Sampling (CVS) system.
Due to the long averaging cycle of such analysers typically taking a sample rate of 1 sample per second for averaging the whole test cycle to be represented in grams per kilometer/mile whereby the change of concentration of gases CO and NOX, which can indicate that a vehicle is under closed loop fuel control adjustment, would not show up under the traditional dynamometer emission testing.
In addition, none of the remote sensing systems of the prior art seems to take the transient operation of the ECU into account whereby rendering the readings taken therefrom to be inaccurate.
As for diesel smoke emission of diesel vehicle, various Diesel Smoke Emission opacity measurement standards and equipments are in use today, wherein all existing smoke tests equipments are coupled closely to the exhaust outlet of a vehicle under test. However, the use of remote sensing technique for the measurement of diesel smoke emission or particulate matter (PM) seems to be a very practical way as the vehicles have to be tested under normal driving condition. Nowadays all the remote sensing devices can make use of the TV spectrum to measure PM at the size around 200-230 nm but the majority of visible ‘smoke’ or PM from the diesel engine is normally represented at the size of 532 nm which is preferably sensed with green light with wavelength around 532 nm. However, there are no correlations between 530 nm and 200 nm PM produced by the combustion due to the nature of diesel engine.
Further, the remote exhaust emission sensing devices of prior art require periodical calibration during operation. The calibration will be carried out after completion of system setup and will also be required every one to two hours thereafter whereby ensuring that the readings obtained to be fallen into a specific range, if not, an adjustment can be correspondingly made for ensuring the quality thereof. Some manufacturers will carry out an initial calibration during start up process and then perform a series of calibration checks by spraying calibration gas in front of the device to see if the initial calibration has been deviated from the predetermined level with a tolerance as high as 30%. In practice such calibrations have to take place while there is enough time gap or clear space between each of the vehicles passing by such that the vehicle emissions can be dispersed substantially thereby not interfering with the calibration gas during such calibration checks. If such calibration checks and recalibration of the device cannot be successfully performed as required, the readings taken may be faulty and unusable as the overall gas readings would be severely affected by the emission from the vehicles passing by.
In fact, it is hard to perform such calibration under a variety of circumstances, especially during heavy traffic condition. In general, it will require at least 10 seconds gap between vehicles passing by. The timing of the release of calibration gas is very critical as the ambient readings will still be affected from the vehicle emissions just passed if the calibration gas was released too early. It is undesirable for using such contaminated value in the calibration process as it will eventually lead to inaccurate emission detections.
Further, the remote exhaust emission sensing systems of prior art might comprise a speed and acceleration unit for measuring the speed and acceleration of the vehicles under test, wherein a number of laser beams separately disposed from each other at a known distance. Such beams may be directed across the road and one or more reflectors can be disposed at either or both sides to reflect the light beams back to a detector at the opposite side of the road. When motor vehicle is passing by the system, the tyres will cut and interrupt the 1st beam and then the 2nd beam. The time difference therebetween or the time of interruption can be used to calculate the speed and the acceleration of the vehicle. Normally the vehicle is presumed to be a pre-specified length and contains only two axles and the front axle tyre and rear axle tyre will produce two time readings for use in the calculation of the speed and acceleration. However, some problems in obtaining the speed and acceleration readings may arise for those vehicles with 3 or more axles.
In fact, several disadvantages with these designs of prior art are known. Firstly, it is time consuming in setting up those reflectors or laser beams on either or both sides of the road as critical alignment is required and must be maintained properly on vibrating roads whereby frequent checking on the alignment thereof is necessary, especially in days with high winds. In addition, the use and deployment of such extra equipments on the road can potentially become a safety hazard to the road users. Further, low profile tyres, motor cycles, trucks with three or more axles and objects hanging down from the vehicles will interfere and produce false triggers to such equipments with old designs whereby leading to a miss or an abnormal number in the speed and acceleration reading. As such equipments sometimes cannot correctly determine the rear end of the vehicle for at least the above reasons, a license plate picture of the vehicle passing by is thus cannot be successfully obtained by corresponding associated equipments whereby rendering the performance of the whole system to be adversely affected. Further, as the wheel base distance is estimated and used in the calculation of the speed and acceleration but an estimation of a fixed wheel base length of passing vehicle will incur errors in the results of the calculation.
Further, remote sensing systems of the prior art are normally powered by mains electricity or have the electrical power being supplied from a gasoline or diesel engine generator when working in the field. In general, such generators have a less sophisticated emission control system than that of the vehicles being under test and are very noisy and heavy thereby they have to be placed at a distance from the test site. This also prevents engine emission and engine noise reaching the test site but such engine emission in fact can eventually pollute the test site due to localized climatical changes in wind directions. The exhaust emissions expelled from the engine generator into the background are thus undesirable in measuring emissions of vehicles passing through the system. In addition, such a power supply system also requires long and heavy power cables to reach the remote sensing test site. Some remote sensing systems have such a generator built into a custom made van, which is very expensive and requires extensive modifications to the van. The parking location of the van will be also restricted as it is not always possible to be parked nearby the testing location of the remote sensing equipment.
Also, some remote sensing systems of the prior art are being controlled by a PC, which is connected to the remote sensing device by a series of long and heavy cables. Motorists seeing such cables' or abnormal devices with wires running from boxes leading to a van or table of equipment would tend to change their driving pattern slightly while they were traveling the road under test conditions. This can be due to their curiosity to observe the event or out of fear that it may be a speed trap or other enforcement device.